﻿CONCLUDING REMARKS. 



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perseverance of our naturalists in dredging the extensive stretch of sea which, extending 

 over 12 degrees of latitude, surrounds the British isles. In making these comparisons, 

 moreover, it should not be overlooked that we contrast results obtained from a patch of 

 fossil sea bottom only a few yards square in Suffolk, 1 with results obtained from the vast 

 area surrounding the British islands. If instead of this a comparison could be instituted 

 between the Coralline Crag fauna and that which might be obtained from an exhaustive 

 dredging of the bottom of the North Sea off the Suffolk coast, my belief is that the exotic 

 character of the Coralline Crag sea would become much more apparent. 



How far during the intercourse which has gone on by ships between Britain and 

 the Mediterranean and Lusitanian coasts for 2000 years past, Mediterranean and 

 Lusitanian Mollusca have been introduced into British waters through the agency of the 

 bottoms, anchors, and especially the ballast of ships, it would be rash to conjecture ; but 

 the extent of this cannot have been inconsiderable, especially during the last two centuries. 

 Whatever the degree to which this has extended may be, it has by so much reduced the 

 exclusively Mediterranean and Lusitanian proportion of the Coralline Crag Mollusca 

 below its real amount. Of course the same process must have had similar results in 

 introducing British species into Lusitanian and Mediterranean waters. 



The numerous species and profusion of individuals of the genus Astarte, the 

 presence of the genus Cyprina, and of such shells as Trichotropis borealis and 

 Glycimeris anyusta, represent, on the one hand, what would be urged in support of the 

 arctic and boreal features of the Coralline Crag fauna. On the other hand, the profusion 

 of such species as Limopsis pygmcea, Cardita senilis, Cardita cordis, Ringicula buccinea, 

 Woodia digitaria, and Dentalium dentalis, and the occurrence of the sixteen genera 

 presently enumerated, represent the Mediterranean features. Besides these we have the 

 tropical forms, Pyrula and Pholadomya, which were probably present as lingerers 

 from those periods anterior to the Crag which are clearly shown by their fossils to 

 have been more and more tropical as we recede in Tertiary time. Although the genus 

 Astarte among recent shells is looked upon as indicating boreal conditions in our present 

 seas, inasmuch as only one species lives in the Mediterranean, yet as we recede in 

 geological time this indication becomes weakened if not negatived altogether, and a proof 

 is afforded that the genus did not in older Tertiary periods originate in icy seas. Thus in 

 the Eocene of England we have no less than four species of this genus in association with 

 such an undoubted tropical Mollusc as the Nautilus ; and of these, two are from the 

 London clay, the climate of which is proved to have been warm not merely by its Nautili, 

 but by the tropical character of the vegetation yielded by the Sheppey deposit. In 

 Mesozoic formations the genus goes back in some abundance of species as far as the Lias 

 in association with gigantic reptilia, through climates indicated by the Purbeck vegetation 



1 To any objection that such a dredging would not disclose the contents of the North Sea bed vertically* 

 I reply that there are but very few Coralline Crag species which I have not found within a vertical range of 

 three feet in the stackyard pit at Sutton. 



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